Turbines whose bottom part and top part of the inner casing are held together by means of the shrink-ring technique are known. This technique has proved successful in turbines having higher pressures and is in particular considered to be cost-effective. The shrink rings are used in those turbines whose taper angles (of the blading duct) are small, namely in high-pressure turbines, intermediate-pressure turbines or combined high-pressure/intermediate-pressure turbines accommodated in a common casing. (In contrast to turbines having higher pressures, flanged or screwed connections are more likely to be used in low-pressure turbines.)
A plurality of such shrink rings are typically arranged at regular intervals. The invention described here, then, relates in particular to the shrink-ring technique in the region of a bleed point of the turbine.
To assist the operation of apparatuses such as feed heaters or a boiler, steam is bled from the turbine and is directed via a pipeline out of the turbine casing to the apparatuses mentioned. To this end, a bleed slot, which leads through the inner casing into the space between inner and outer casings, is arranged at the outer contour of the blade duct of the turbine. The steam flows from the blade duct of the turbine through the bleed slot and is collected in a sealed-off annular space, which is formed above the bleed slot by a cast bleed ring in the form of a collar on the outer surface of the inner casing. This bleed ring is fastened to the inner casing in a sealing manner. Arranged on the ring is a pipe connection which leads through the outer casing to the outside and is connected to a pipeline, which leads to a feed heater, boiler or other thermal apparatus.
The shrink rings and the bleed ring are each fixed to the inner casing by a plurality of bolts and screws, so that the rings cannot be displaced relative to the casing.
A disadvantage with this prior art is that a plurality of components and small parts, which are individually produced and fitted, are required for the bleeding and for holding together the inner casing by means of shrink rings in the region of the bleed point. In particular, the manufacture of a cast bleed ring requires several production steps. Finally, for the many components and small parts required, this means a long fabrication and assembly time and resulting high costs.